firewire: ohci: do not clear PHY interrupt status inadvertently

The interrupt status bits in PHY register 5 are cleared by writing a one
bit.  To avoid clearing them unadvertently, do not write them back when
they were read as set, but only when they have been explicitly requested
to be set.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
diff --git a/drivers/firewire/core.h b/drivers/firewire/core.h
index fb03213..b2a7b65 100644
--- a/drivers/firewire/core.h
+++ b/drivers/firewire/core.h
@@ -28,6 +28,7 @@
 #define PHY_CONTENDER		0x40
 #define PHY_BUS_RESET		0x40
 #define PHY_BUS_SHORT_RESET	0x40
+#define PHY_INT_STATUS_BITS	0x3c
 
 #define BANDWIDTH_AVAILABLE_INITIAL	4915
 #define BROADCAST_CHANNEL_INITIAL	(1 << 31 | 31)